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用于在velocity中实现模板的继承，包含 block,override,extends指令
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父模板：base.vm
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http://badqiu.iteye.com/blog/558194
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在velocity的properties中增加如下配置以激活自定义指定
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userdirective=com.baomidou.velocity.directive.BlockDirective,com.baomidou.velocity.directive.OverrideDirective,com.baomidou.velocity.directive.ExtendsDirective
<br/>缓存开启<br/>
file.resource.loader.cache = true
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